Conventionally, methods for analyzing diverse types of samples, and determining various characteristics of such samples using current measurement techniques, have been under development.
For example, techniques for analysis of DNA nucleotide sequences are used not only in scientific research, but also in numerous other fields, such as in medical treatment, drug development, and criminal investigation, with increasing interest in the development of such techniques. Therefore, previously, techniques are being developed for analyzing DNA nucleotide sequences by measuring electrical current.
For example, techniques are being developed for performing sequencing employing a single molecule of DNA, by detecting short-lived interruptions in ionic current that occur as a single-stranded DNA passes through nanopores formed by proteins embedded in cyclodextrin (see, for example, Non-patent Documents 1 and 2).
However, these techniques have many issues, such as: (1) pore size cannot be changed; and (2) such systems are unstable since the nanopores are formed by proteins. The development of techniques different from such techniques has therefore been desired.
Under these circumstances, a sequencing theory has been proposed based on transverse electron transport. This theory is based on principles regarding detection of a characteristic transverse conductivity of each nucleotide as nucleotides pass through the interior of a nanoscale space between a pair of electrodes. This conductivity relates to the different HOMO-LUMO gap of each nucleotide.
Specifically, when single-stranded DNA passes through a nanopore interior, a tunneling current is produced between an electrode pair, the electrode pair having a nanoscale interelectrode distance and provided at the edges of the nanopore, through each nucleotide constituting the single-stranded DNA. Then, each of the nucleotides constituting the single-stranded DNA can be directly identified, without labeling, by measuring the current value of the tunneling current (see, for example, Patent Document 1).